Can I build a screen reg. with IXYS 10M45? - diyAudio
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Old 17th September 2012, 04:17 PM   #1
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Default Can I build a screen reg. with IXYS 10M45?

That is the question. I am building another EL84 P-P amp and my old japanese outputs have no screen taps. I need a little more power this time so I dont want to go triode and I have always heard that regulated screens will have great benefits WRT linearity as opposed to just a resistor and cap solution. I am quite inept when it comes to playing in the "sand-box" but I have used 10M45S for active plate loads and in LTP's. Is a CCS for screens doable or is this not really "regulation" Any advice would be appreciated.
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Old 17th September 2012, 04:21 PM   #2
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You need a regulator, not a CCS.
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Old 17th September 2012, 04:43 PM   #3
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Ok, Thanks. I had a feeling. Some part of my brain thought that giving them a constant current would somehow "regulate" them. Can anyone recommend a fairly simple reg.? I have been looking at the "red-light district for example...
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Old 17th September 2012, 05:19 PM   #4
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You can use RDL's regulator. Pretty easy. Well explained at SY's webpage. I have done it with no problems
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Old 17th September 2012, 10:38 PM   #5
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This will work , if you stay in its limits , OTB - A Solid-State Filter Choke or Field Coil Replacement
I would use a BU508A in place of the tip 50
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Old 18th September 2012, 09:27 AM   #6
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Ofcourse you can build screen regulator with IXYS 10M45 or with some dozens of other types of NFET.

Below is one circuit I have used. If the adjusting range needs to be modified, just adjust R26.

If you stabilize the screen voltage, you should also stabilize -Ug1-voltage or use autobias.

Click the image to open in full size.

Last edited by artosalo; 18th September 2012 at 09:35 AM. Reason: Typo
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Old 18th September 2012, 10:26 AM   #7
DF96 is offline DF96  England
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A pentode with a CCS feeding the screen would behave a bit like a triode, but probably with more distortion. Perhaps someone should try it - could start a new fashion!
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Old 18th September 2012, 03:28 PM   #8
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To avoid misunderstanding of any sort, my schematic above is a voltage regulator, not constant current source.
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Old 18th September 2012, 06:16 PM   #9
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Smile Obstinate Little Sister

Quote:
Originally Posted by DF96 View Post
A pentode with a CCS feeding the screen would behave a bit like a triode, but probably with more distortion. Perhaps someone should try it - could start a new fashion!
Hello,

Just going along with the “what if” a CCS was connected to the screen of a pentode, with all things constant there would be a fixed voltage on the screen.

If the pentode is connected as a triode the screen is strapped to the plate, as the plate voltage changes the screen voltage is equal. Strapped as a triode the screen is more like a me too little brother plate and follows along.

Seems to me with the screen connected to a CCS it would behave more like an obstinate little sister. It will have a “plate” resistance of its own. With a constant current operating into a constant resistance it sounds like a pentode like constant screen voltage to me. Added (Perhaps a not so constant little sister plate resistance producing a sort of ultra-linear effect)

Dave this is just for fun musing, not an argument. Yes someone should try it!

DT

Last edited by DualTriode; 18th September 2012 at 06:28 PM. Reason: Added
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Old 18th September 2012, 06:45 PM   #10
DF96 is offline DF96  England
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In most pentodes the screen current is roughly a constant proportion of the anode current. So as the control grid tries to change the current the screen grid will fight back, just like a high impedance load does for a triode. The screen voltage will change roughly according to the inner mu (g1-g2), and anode voltage will follow. Gain will be low, but it might be more linear than the bare pentode.

Big snag is that at lower anode voltages things change. As the anode goes lower in voltage the screen picks up a greater proportion of the total current. At least, it would but it can't because of the CCS so instead the screen voltage drops so the current change is forced to the anode. I think this could mean a boost in anode gain at low anode voltages. My guess is a boost in higher order distortion.
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